There is an ever-increasing need for electronic devices and systems having improved reliability. One potential source of failure for an electronic system is its cooling system. The electronic components of such systems typically generate a considerable amount of heat in an enclosed or semi-enclosed space. It is often necessary to provide a cooling system in order to prevent temperature gradients that could compromise the function of such electronic components.
One method of cooling is the use of an air mover such as a fan or impeller in order to establish air flow across the electronic components. Such air flow facilitates the dissipation of generated heat by convection heat transfer. In some cooling systems, multiple air movers are mounted in a bank arrangement wherein each of the air movers moves a portion of the air that is being used to cool the electronic system, and the air movers in combination provide the cooling capacity necessary to cool the electronic system.
One or more air movers are sometimes mounted to move air along an air flow path to cool electronic components that are oriented in series along that path. This is not to say that the electronic components are connected in series or arranged directly along the air flow path in the geometric sense; instead, such serial orientation refers to the general movement of the air flow across the electronic components in such a way that portions of the same stream of air bring about the required heat transfer from substantially all of the electronic components.
In such serially cooled environments, there is often an accumulation of heat as the air moves across the electronic components. In other words, the temperature gradient increases along the air flow path so that the temperature of exhaust air can be substantially higher than that of the inlet air.
In recent years, there has been a trend in the high end server market to utilize standard personal computer (PC) components to assemble larger server systems. The cost associated with the development of custom components has become increasingly prohibitive when compared to the increasing performance of PC's. Moreover, the large volume of PC's keeps the cost of these components at a minimum.
As the frequency of the processors used in such server systems continues to increase, the power level of the components continues to climb. Also, as the speeds of the components increase, the minimization of the distance between the components becomes more and more critical. The increased power level and reduced distance between components are factors that combine to make it very difficult to cool such components effectively. Although with single processor machines such as PC's even high-powered processors can be fairly easily cooled with the use of active fan sinks on the processors, the reliability and serviceability of the such active components prohibit their use in a high end server. For example, in large servers it is quite challenging to package components such as those designed for PC's into large systems. Since the geometry of such components was developed with the PC in mind, they may not be conducive to packaging into large, densely packed, high end servers.
Typically, large high end servers include printed circuit boards that are arranged in card racks of parallel banks of cards. Such cards can be cooled relatively easily by blowing or drawing air through the banks of cards. Serially cooled system cabinet level coolers can provide a cost-effective means to cool an entire enclosure. Also, such cabinet level cooling schemes make it easy to provide redundant cooling for the system. Furthermore, such cooling schemes make it easier to provide hot maintenance of the cooling system.
However, using PC components, the geometry's of the various assemblies end up in many different orientations that make traditional serial cooling techniques difficult or impossible. Also, these high end servers use multiple processors to gain performance and such processors all need to be kept very close to each other, close to the cache, and to the bus interface devices and the main system memory which can create high power density in tightly-packed areas.
Various cooling schemes have been proposed over the years. For example, in U.S. Pat. No. 4,528,614, Shariff et al. describe switchgear units housed in a cabinet having an integral air-ventilation duct system of modular snap-fitting construction having an air intake opening at the bottom of the cabinet, an air exhaust opening at the top of the cabinet, and branch ducts that communicate with tandem compartments that are in stacked relationship. The ventilation duct assemblies have a vertically extending duct and a series of transverse branch ducts.
In U.S. Pat. No. 4,774,631, Okuyama et al. describe a cooling structure having shelf units wherein a fan unit is disposed on top of each shelf to constitute a separate cooling block. The fan unit of each cooling block generates a cooling wind which is passed linearly through the shelf unit from the bottom to the top as well as introducing atmosphere through vent holes formed in side face portions of each fan unit. The flow rate of the cooling wind will be gradually increased as the cooling wind proceeds to the upper cooling blocks.
In U.S. Pat. No. 5,361,188, Kondou et al. describe a cooling apparatus having a comb-tooth shaped duct for defining flow paths along substrates to introduce cooling air to each integrated circuit device. The duct includes small holes at positions corresponding to the integrated circuit devices and having open areas corresponding to the heating values of the integrated circuit devices.
Despite the various attempts to develop improved cooling systems in the past, there remains a need for an improved cooling system for use in connection with electronic systems such as large, densely packed high end servers. Accordingly, it is an object of this invention to provide an improved cooling system that can be used in order to improve the reliability, availability, and serviceability of such electronic systems.